Electro‑crystallized NiO nanoparticles for river‑water treatment applications

There is a fundamental relationship between properties of nanoparticles and their preparation method. In this study, NiO nanoparticles were electro-crystallized in an electrochemical cell containing two nickel electrodes, and an electrolyte solution of tetramethylammonium chloride and NaOH. The optimized reaction parameters obtained for the effective electro-crystallization of NiO nanoparticles were applied potential of 10 V, electrolyte concentration of 0.075 M, bath temperature of 20 °C, and annealing temperature of 400 °C. XRD results approved the formation of cubic structure of NiO. SEM images showed the mean particle size of spherical particles ranging from 12 to 47 nm. Based on UV–visible results, the value of band gap for typical NiO nanoparticles was obtained ~ 3.56 eV. The photoluminescence spectrum of a typical NiO sample showed two peaks at 370 nm and 670 nm, related to 3d8 electron transition, recombination between electrons and holes, or defects in NiO nanoparticles. The magnetization curves showed that all samples are magnetically soft and the specific magnetization is dependent on the particle size. The electro-oxidation of Ni was particularly effective for cobalt and cadmium removal from laboratory water at high voltages. This protocol was also successful for removing cobalt and cadmium from two rivers in Iran. Based on atomic absorption spectroscopy analysis, it is possible to remove ~ 100% of cobalt and cadmium from water using obtained nanoparticles. The method could be economically scaled up to industrial capacity.